Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Another goal of semiconductor manufacturing is to produce higher performance semiconductor devices. Increases in device performance can be accomplished by forming active components that are capable of operating at higher speeds. In high frequency applications, such as radio frequency (RF) wireless communications, integrated passive devices (IPDs) are often contained within the semiconductor device. Examples of IPDs include resistors, capacitors, and inductors. A typical RF system requires multiple IPDs in one or more semiconductor packages to perform the necessary electrical functions.
In a wireless RF system, an RF front end module (FEM) is coupled to an antenna for transmission and reception of wireless RF signals. The RF FEM separates and filters the transmit RF signal and receive RF signal to avoid conflict or cross-over between the RF signals. The separated transmit RF signal and receive RF signal are routed to or received from an RF transceiver for demodulation and conversion to baseband signals for further signal processing. The RF system can be part of a cellular telephone, PDA, or other wireless communication device.
FIG. 1 shows a block diagram of a conventional RF FEM 10 coupled to antenna 12. RF FEM 10 has a transmit section and receive section. In the transmit section, the transmit RF signal from the RF transceiver is routed to an input of power amplifier 14 to increase signal power and amplification. The output of power amplifier 14 is coupled to RF coupler 15 which detects the transmit signal power level. The transmit RF signal is filtered by LC filter 16 and routed to TX/RX switch 18 which switches between the transmit RF signal and receive RF signal. When selected by TX/RX switch 18, the transmit RF signal is routed to diplexer 20 which performs frequency multiplexing from two ports to one port for transmission by antenna 12.
In the receive section, the receive RF signal from antenna 12 is processed through diplexer 20 for frequency de-multiplexing from one port to two ports. When selected by TX/RX switch 18, the receive RF signal is routed to surface acoustic wave (SAW) filter 22. SAW filter 22 converts an electrical signal to a mechanical wave using a piezoelectric crystal or ceramic. The mechanical wave is delayed by the piezoelectric structure to provide a narrow pass-band response by rejecting out-of-band signals. The filtered wave is converted back to an electrical signal and routed to the RF transceiver as the receive RF signal.
FIG. 2 shows a conventional semiconductor package 23 for implementing RF FEM 10. Substrate 24 is a multilayered low temperature co-fire ceramic (LTCC) laminate with a plurality of internal dielectric layers 26 and conductivity layers 28, such as silver or copper. LTCC substrate 24 includes internal passive components, such as resistor 30, capacitors 32, and inductors 34, as well as embedded RF circuits 36, within the multilayered substrate. A TX/RX switch die 38 and discrete resistor 40 are mounted to a top surface of LTCC substrate 24 and electrically connected to conductive layers 28. A SAW filter die 42 is mounted to LTCC substrate 24 and electrically connected to conductive layers 28. SAW filter 42 is relatively large due to its mechanical features, but can be placed in a recess formed in LTCC substrate 24 in an attempt to reduce the height of semiconductor package 23.
RF FEM 10, as implemented semiconductor package 23 with SAW filter die 42, represents a relatively bulky and complex structure and involves high manufacturing costs. As the demand for smaller packages and lower cost drives the market, additional work is needed to improve the RF FEM design.